According to Imogen Heap, a little known singing artist starting to gain popularity now, the new Britney song 'Over To You Now' was recorded by Britney in 2003 for the album In The Zone and the song was also produced by Guy Sigsworth with Imogen laying down the background vocals. Here's what Imogen Heap had to say about the song on her official site:
Guy and i did the song for Britney about a year ago.
I didn't meet her, but Guy asked me into the studio to throw down some ideas as she was coming in a couple of days after to do the song "Everytime" with him. Her record company wanted a couple of other too. Guy did end up using quite a lot of my vocals! I hear he's quite a fan of my voice...